Pressure adjustment method for CPAP machine

ABSTRACT

A positive airway pressure apparatus is automatically adjusting. Pressure increases in response to apnea events when the apparatus is in one or more responsive states. Pressure does not increase in response to apnea events when the apparatus is in a non-responsive state. The apparatus switches between responsive and nonresponsive states depending upon any of a number of different criteria that help differentiate between open airway apnea events and closed airway apnea events.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/868,713, filed Jan. 11, 2018, now U.S. Pat. No. 11,077,267, which isa continuation of U.S. patent application Ser. No. 15/153,278, filed May12, 2016, now U.S. Pat. No. 9,895,506, which is a continuation of U.S.patent application Ser. No. 14/673,242, filed Mar. 30, 2015, now U.S.Pat. No. 9,339,619, which is a continuation of U.S. patent applicationSer. No. 12/975,015, filed Dec. 21, 2010, now U.S. Pat. No. 8,991,392,each of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to systems for treating obstructive sleepapnea by providing positive airway pressure to a patient, in particular,to methods for the device to adjust the treatment pressure in responseto breathing events.

Description of the Related Art

One major treatment approach for obstructive sleep apnea includesproviding breathing gases to the patient throughout the period thepatient is asleep. These treatments may collectively be known aspositive airway pressure therapy (PAP). Variations on this therapyinclude having different inspiration and expiration pressures, commonlyknown as bi-level or bi-PAP, or having continuously adjusting therapywhich responds to breathing events.

Self-adjusting or self-titrating PAP systems typically increase thetreatment pressure in response to events, and decrease the treatmentpressure in response to periods of normal breathing. Events for whichthe systems increase pressure can include apneas, hypopneas andobstructed breathing. Many different methods have been provided fordetermining the occurrence of an apnea, a hypopnea or obstructedbreathing. For example, our U.S. patent application Ser. No. 11/198,072describes a system that determines events by analysing a flow signalprovided by a flow sensor. The system determines an apnea based on aperiod where the flow signal indicates a lack of patient breathing. Thesystem determines a hypopnea based on a period of reduced breathingvolume. The system determines obstructed breathing on analysis of thediscreet energy spectrum of the flow signal of patient breaths. Thesystem modifies the treatment pressure depending on the present pressureand the determined event. When responding to apneas or hypopneas, thedescribed system only increases the pressure if the present treatmentpressure is below 10cmH2O. When responding to flow limitations andobstruction, the system will always increase pressure, subject to anoverall maximum allowed pressure.

An upper limit for responding to apneas and hypopneas that are notaccompanied by a flow limitation is to recognise that not all events arecaused by obstruction and collapsing airways which can be alleviatedwith increased pressure. Instead, some events, commonly referred to as“central” events, do not respond to increases in pressure. Many CPAPpatients suffer from both obstructive events and central events.Although increasing the treatment pressure in response to central eventsis not usually dangerous, it is believed that it could triggeradditional central events or rouse the patient. This is generallythought more likely with higher CPAP pressures, and the likelihood thatan event is central is generally thought more likely at higher treatmentpressures.

Nonetheless, a defined threshold may not be the optimal solution fordeciding whether to increase the pressure in relation to apneas and nonflow-limited hypopneas. In some cases, where central apneas are beingexperienced at lower pressures, this system will allow the CPAP pressureto reach a level that is not required. In other cases, the thresholdpressure may be reached with the patient still incurring obstructedapneas that could respond to further increases in pressure.

Methods have been devised to attempt to differentiate between openairway apneas, which are unlikely to respond to increases in PAPpressure and closed airway apneas, which may respond to an increase intherapy pressure. These include analysing the flow in pressure signalsto determine the presence of airflow, that is airflow that is generatedby the beating heart which can slightly affect the lung volume. Anothermethod involves examining the airway response to a forced oscillation orprobing signal. Both these methods add complexity to the system and maynot be fully reliable across a wide range of patients.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a control method, or aPAP system including a control method, which goes some way towardovercoming the above disadvantages or which will at least provide thepublic with a useful choice.

In one aspect, the present invention may broadly be sid to consist in anapparatus comprising a gases flow source including a blower supplying anoutlet which in use is connected to a patient, a sensor for sensingpressure or flow or both, supplied by the blower, a controller receivingoutput from the sensor, and controlling the output of the blower, thecontroller determining at least apnea, non-flow limited hypopnea, orflow limited breaths from the output of the sensor, the controllerperforming a control method including a sequence of states in which thecontroller will or will not respond to non-isloated apneas by increasingthe output of the blower, the sequence including at least two responsivestates in which the controller may respond to an apnea, or to a non-flowlimited hypopnea or to a flow limited breath by increasing pressure, butin the case of an apnea only when the apnea was preceded within adefined period by another apnea or a non-flow limited hypopnea, at leasttwo non-responsive states in which it will not respond to an apneaincreasing pressure; the control method switches from responsive statesto non-responsive states according to function of both elapses of timein the responsive state without events, and accumulated apneas andnon-flow limited hypopneas since entering the responsive state; thecontrol method switches from a first non-responsive state to aresponsive state by one or more of the following elapse of time in thenon-responsive state, sensing patient arousal, elapse of time withoutapneaic events; and the control method switches from a secondnon-responsive state to a responsive state by one or more of thefollowing elapse of time in the non-responsive state, sensing patientarousal and not based only on a elapse of time without apneic events;such that a long sequence of consecutive non-isolated apneas leads thecontrol to adopt, in order, a responsive state, the first non-responsivestate, another responsive state and the second non-responsive state; andresults in a first sequence of output increases, a pause, a secondsequence of output increases and then an indefinite suppression offurther increases.

In a further aspect, the present invention may broadly be said toconsist in an apparatus comprising a gases flow source supplying anoutlet which in use is connected to a patient, a sensor for sensingpressure or flow or both, supplied by the flow source or supplied to thepatient, a controller receiving output from the sensor, and controllingthe output of the flow source, the controller determining at least apneaevents from the output of the sensor, the controller performing acontrol method including one or more responsive states in which it mayrespond to an apneaic event by increasing pressure, non-responsivestates in which it will not respond to an apneaic event by increasingpressure; the control method switches from a non-responsive state to aresponsive state by one or more of the following, depending on theresponsive state elapse of time in the non-responsive state, sensingpatient arousal, elapse of time without apneaic events; and the controlmethod switches from a responsive state to a non-responsive state by afunction of both: elapse of time in the responsive state without events,and accumulated apneaic events since entering the responsive state.

According to a further aspect, the gases flow source comprises a blowerand the output of the blower is controlled by the controller.

According to a further aspect, the gases flow source includes ahumidifier and power input to the humidifier is controlled by thecontroller.

According to a further aspect, the sensor is a flow sensor.

According to a further aspect, the controller maintains desired pressuredata representing a desired treatment pressure and the controllercontrols the output of the source according to the desired pressuredata.

According to a further aspect, the apparatus includes a pressure sensorfor sensing pressure supplied by the flow source and the controllercontrols the output of the flow source with a feedback control tomaintain the output according to the desired pressure data.

According to a further aspect, apneaic events include apnea and non-flowlimited hypopnea.

According to a further aspect, the controller also determines flowlimited breaths, and responds to determinations of flow limited breathswith increases in pressure.

According to a further aspect, the apparatus includes two differentresponse states, one of which may be followed by a first non-responsivestate that can be exited by lapse of time (with or without apneaicevents), and the other is entered from the first non-responsive state.

According to a further aspect, the other response state may be followedby a non-responsive state that can only be exited by elapse of timewithout apneaic events, or by sensing patient arousal.

According to a further aspect, the controller responds to an apneaicevent only if it is preceded by another apneaic event in a definedperiod.

According to a further aspect, the defined period is between 2 minutesand 3 minutes.

According to a further aspect, the controller will respond to flowlimited breaths in both the responsive and non-responsive states.

According to a further aspect, for one non-responsive state, thecontroller will exit the non-responsive state after an elapse of between3 and 7 minutes (with or without apneaic events).

According to a further aspect, the controller exiting a non-responsivestate in response to patient arousal also reduces the delivered therapypressure.

According to a further aspect, the controller will exit a non-responsivestate due to an elapse of time without apneaic events once the desiredpressure level returns to a minimum pressure.

According to a further aspect, the controller switches from a responsivestate to a non-responsive state if an accumulation of non-isolatedapneaic events exceeds an accumulation of normal breathing by apredetermined amount.

According to a further aspect, in the absence of nominal periods ofnormal breathing, the predetermined amount triggers a non-responsiveperiod after three non-isolated events.

According to a further aspect, the controller reduces the pressure by0.5cmH₂O each 2.5 minute period without events.

According to a further aspect, the controller raises the pressure by anincrease of 1cmH₂O when responding to an apneaic event.

In a further aspect, the present invention may broadly be said toconsist in a control method for a controller in an automaticallyadjusting PAP apparatus, including one or more responsive states inwhich it may respond to an apneaic event by increasing pressure;non-responsive states in which it will not respond to an apneaic eventby increasing pressure; the control method switches from anon-responsive state to a responsive state by one or more of thefollowing, depending on the responsive state elapse of time in thenon-responsive state, sensing patient arousal, elapse of time withoutapneaic events; and the control method switches from a responsive stateto a non-responsive state by a function of both elapse of time in theresponsive state without events, and accumulated apneaic events sinceentering the responsive state.

The term “comprising” is used in the specification and claims, means“consisting at least in part of”. When interpreting a statement in thisspecification and claims that includes “comprising”, features other thanthat or those prefaced by the term may also be present. Related termssuch as “comprise” and “comprises” are to be interpreted in the samemanner.

In this specification where reference has been made to patentspecifications, other external documents, or other sources ofinformation, this is generally for the purpose of providing a contextfor discussing the features of the invention. Unless specifically statedotherwise, reference to such external documents is not to be construedas an admission that such documents, or such sources of information, inany jurisdiction, are prior art, or form part of the common generalknowledge in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

One preferred embodiment of the present invention will be described withreference to the accompanying drawings.

FIG. 1 is an illustration of a patient receiving PAP therapy from asystem including a flow generator, a patient interface and a conduitconnecting between the patient interface and the flow generator.

FIG. 2 is a schematic diagram illustrating an overall pressure adjustingalgorithm.

FIGS. 3 a to 3 c is a schematic diagram illustrating an algorithm thatadjusts the response to apneas.

FIGS. 4 a to 4 c are plots of pressure against time illustrating theeffect of sequences of events on the delivered therapy pressure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to particular aspects of a self-adjustingtherapy device. In particular, the present invention provides controlprinciples that adapt how the device adjusts the treatment pressure inresponse to apneas and non flow-limited hypopneas. One principle of thiscontrol is that the response to apneas and non flow-limited hypopneasoperate independently to the response for other events, including flowlimited breaths and flow-limited hypopneas and periods of normalbreathing.

According to this control strategy for apneas and non flow-limitedhypopneas, certain patterns of events are determined and responded to byentering a non-responsive state. In the non-responsive state, thecontrol will not increase the treatment pressure in response to anotherapnea, but will increase the treatment pressure in response to any otherevent including flow-limited breaths, flow-limited hypopneas or nonflow-limited hypopneas. Preferably, the control provides an independentpressure limit for the response to non flow-limited hypopneas.

According to another principle, the control does not respond to isolatedapneas. The control will only respond to an apnea if the apnea occurswithin a predetermined time of another apnea or within a predeterminedtime of a non flow-limited hypopnea.

According to another principle, the device provides a limited responseto a string of rapidly occurring apneas or non flow-limited hypopneas.In particular, the control enters a pause state if the total number ofnon isolated apneas and hypopneas less any number of nominal periods ofnormal breathing exceeds a threshold value, for example, “3”. Thisthreshold is not directly related to any pressure increase. Pressureincreases over this period may have been larger due to additionalflow-limited events or smaller, due to the limit on response to nonflow-limited hyponeas.

According to a further principle, the control will respond to two suchchains of apnea, with an intervening pause state, and then enter alonger term non-responsive state. The longer term non-responsive statewill inhibit response to apneas until the set pressure reduces below athreshold, due to periods of normal breathing.

To understand the effect of this control, the control must be consideredas an overlay on the concurrent responses being provided to normalbreathing, obstructed breathing, flow-limited hypopneas and nonflow-limited hypopneas.

In the preferred control, the only limitation to response toflow-limited breaths is an overall maximum therapy pressure. Thisapplies also to flow-limited hypopneas. The only limitation on responseto non flow-limited hypopneas is a pressure limit operatingindependently of the apnea control.

According to this, the apnea response algorithm can operate quiteindependently of how the device responds to other OSA events. An exampleapnea response algorithm will be described on that basis. This algorithmis illustrated in FIG. 4 and is indicated by box 284 in FIG. 2 . Asindicated in FIG. 2 , the apnea response process 284 operates as aperiodic control loop that sits between an event detection procedure 282and a pressure adjustment procedure 286. The event detection loop 282provides an event variable (Event), or a set of event flags whichindicate the determination of certain OSA events, including apnea, nonflow-limited hypopnea, normal breathing, no event, and other events(which might include flow-limited hypopneas, flow-limited breaths,arousals or snoring).

In the pressure adjusting algorithm 286, the set pressure is incrementedor decremented according to the event variable. Typically, this involvesan increase in pressure for OSA events such as apneas, hypopneas,flow-limited breaths, flow-limited hypopneas and snoring, a decrease inpressure in response to sustained periods of normal breathing or patientarousals, and maintaining the present set pressure when the Eventreturns “none”.

The presently described apnea control sits between the eventdetermination algorithm and the pressure adjustment algorithm andmodifies the value of Event by replacing “apnea” events with “none”under some circumstances.

In considering the described control, it is important to note that theexample algorithm is repeated frequently and rapidly. For example, thefull algorithm might be repeated every 20 ms to 50 ms. This is more thanten times the frequency of patient breathing and means that events otherthan “none” are comparatively rare, and the normal status for the Eventis “none”. For example, in a typical event determination algorithm,“normal breathing” might be returned after a predetermined periodwithout any OSA events or arousals, and this predetermined period mightbe between 2 and 5 minutes. If this predetermined period is 2.5 minutesand the repeat frequency of the apnea response algorithm is 20 ms, thena return of “normal breathing” will be preceded by 7,500 executionswhere the Event is “none”. Similarly, an apnea might be determined inresponse to 10 seconds without a detected breath. During this period,the event determination algorithm may be returning “none”, meaning 500“none” returns.

According to this example, the apnea detection algorithm only returns“apnea” once for any single period of non-breathing. For example, theapnea detection may return “apnea” after a predetermined trigger periodwithout detected breathing. The apnea detection algorithm then returns“none” until breathing resumes or another independent event occurs.

Even a single flow-limited breath would require 1 to 1.5 seconds, andtherefore be preceded by 50 to 75 “none” returns.

The described apnea response algorithm is structured accordingly.However, other control approaches could be developed using theprinciples outlined earlier. For example, the principles could beintegrated into an interrupt-based response system, where a piece ofpressure adjustment code is executed only when an event other than“none” is returned. The adjustment code would then review a history ofevents to determine the outcome for the event concerned.

In most executions of the described apnea response algorithm, there iseither no effect, or the only effect is to decrement a timer by anamount reflecting the time since the previous execution.

The preferred algorithm is illustrated in FIGS. 3 a to 3 c . In thepreferred algorithm, the effect that the algorithm has on the eventvariable depends on an apnea response state. The apnea responsealgorithm maintains the apnea response state as the value of variableNr. The algorithm progressively moves through apnea response states inresponse to particular patterns of apneas and non flow-limitedhypopneas. In each of the apnea response states, the algorithm has aprocess for determining whether to replace an Event equals “apnea” valuewith an Event equals “none” value and whether to increase to the nextresponse state. Independently, a portion of the algorithm has steps fordeciding whether to step back one apnea response state in response to anEvent equals “normal” value. The algorithm also has additionalfunctionality to improve the response to apneas that arise at a timewhen pressure is being relieved due to the sensing of patient arousal orawakening and steps to completely reset the response state if thepressure returns to the minimum set pressure due to periods of normalbreathing.

Looking at the illustrated algorithm in detail, the apnea responsealgorithm is entered at step 401. As noted previously, the algorithm isrun repetitively and, by way of example, might be run every 20 ms.

The algorithm proceeds to step 402 and compares a pressure decreasevariable Pd against a threshold value, for example 3cmH₂O. The pressuredecrease variable represents an amount of decrease that has occurredimmediately recently in relieving pressure in response to sensingpatient arousal or awakening. The subsequent loop, or loops, at steps403 and 404 and a further loop involving steps 490 to 493 determines theeffect that this situation has on the apnea response state and asubsequent pressure increase responding to any new apnea.

In particular, steps 403 and 404 would determine that if the apnearesponse state is greater than 3, then the apnea response state becomes3, the timers (Tc and Tp) used in the apnea response algorithm are resetto 0 and a normal breathing counter Nd is set at 2, requiring twoperiods of normal breathing before reduction will occur in the apnearesponse state. This value for the normal breathing counter isessentially the reset value.

This apnea response state (Nr=3) is a state immediately before thealgorithm will enter a pause state, allowing settling of patientairways. Accordingly, a pair of apnea or non flow-limited hypopneaevents within a triggering time period will then cause the algorithm toenter the pause state but allow the controller to respond to the secondevent.

Returning the apnea response state to 3 in the case of a large pressurereduction following patient arousal brings the algorithm back into astate that can respond to further events.

So at step 402, the algorithm decides whether the recorded pressuredecrease Pd is greater than 3cmH₂O. If so, the algorithm proceeds tostep 404 and decides whether the apnea response state is greater than 3.If it is, then the algorithm proceeds to step 404, resets the apnearesponse state as 3, the normal breathing counter as 2 and the timers as0. If a negative determination is made at step 402 or 403, the algorithmproceeds directly to step 405. Step 404 returns to step 405 afterresetting the variables.

The set of steps 490 to 493 will now be described. This is out of ordercompared to how they occur within the rest of the algorithm. but isconvenient because they also relate to how the algorithm responds in thecase of patient arousal. Essentially, steps 490 to 493 set a customisedpressure increase in response to an apnea (proceded closely by an apneaor non-flow limited hypopnea) that occurs while the pressure is beingdecreased in response to an arousal. In particular, step 490 checkswhether Event equals “apnea”. If Event equals “apnea”, the algorithmproceeds to step 491. Otherwise, the algorithm proceeds onward to step495.

If Event equals “apnea” at step 490, the algorithm proceeds to step 491and checks whether the pressure decrease is greater than 3cmH₂O. If thepressure decrease (so far) due to the arousal is not greater than3cmH₂O, then the subsequent pressure increase Pi is set as 1 cmH₂O.Otherwise, the algorithm proceeds to step 492 and sets the pressureincrease Pi as half the pressure decrease Pd. Steps 492 and 493 returnto step 495 after setting the pressure increase variable Pi. Thepressure increase variable Pi may be used in a subsequent pressureadjustment algorithm to override any alternative determination.

This part of the response is separated from the initial consideration ofthe effect of pressure decrease due to patient arousal at steps 402 to404. These steps may not be triggered immediately, even if theinterrupting event was an apnea, because the event variable may havebeen set from “apnea” to “none” by steps associated with the apnearesponse state. For example, if the arousal triggered step 404, thensubsequent steps 434, 439 and 440 will set event to “none” before theprocess reaches step 490. That will be described.

Returning to consideration of step 405, at step 405, the algorithmdetermines whether Event equals “normal”. Event equals “normal”indicates that the event detection algorithm has determined thatbreathing has been normal, with no sleep disorder events, for animmediately preceding predetermined period of time. In the preferredform, this period of time would be between 2 minutes and 5 minutes, mostpreferably about 2.5 minutes. The event detection algorithm will returnan Event equals “normal” once only before resetting its normal breathingtimer. An Event equals “normal” value will only be returned once each2.5 minutes in the presence of sustained steady breathing.

If the algorithm determines that Event equals “normal” at step 405, thealgorithm proceeds to step 406. At step 406, the algorithm decrementsthe normal breathing counter Nd by 1. The preset state for the normalbreathing counter Nd is 2, and this step represents the only step in theapnea response algorithm which will decrement the normal breathingcounter. Accordingly, the first iteration through step 406, the counterwill be decremented from 2 to 1. On a subsequent occasion, the counterwill be decremented from 1 to 0, unless the counter has been reset to 2in the intervening period. The algorithm proceeds to step 407 anddetermines whether the counter is greater than 0. If the counter isgreater than 0, then the algorithm takes no action and proceeds directlyto step 490. Step 490 would inevitably determine false, and so thealgorithm in fact proceeds to step 495.

The loop at steps 495 and 496 has the purpose of resetting the apnearesponse state when the set pressure drops to the minimum pressure.Changes in the set pressure that lead to the set pressure dropping tothe minimum pressure are made in the pressure adjustment algorithm.These reductions could occur for at least two reasons. The first reasonis periods of normal breathing, indicated by an event equals normalvalue and which usually leads to a decrement to the set pressure Ps. Theother cause of reductions in pressure is in the case of pressure reliefdue to sensed arousals. In that case, pressure is reduced more rapidly,for example about 0.1cmH₂O per second.

At step 495, the apnea response algorithm determines whether the setpressure Ps has reached the minimum pressure Pm by decreases in value.If so, the algorithm proceeds to step 496, otherwise the apnea responsealgorithm exits at step 497. The algorithm will not proceed to step 496on occasions where the set pressure equals the minimum pressure, but wasalready at the minimum pressure in a previous iteration. This ensuresthat the resetting function of step 496 only occurs once and does notoverride the effect of other parts of the apnea response algorithm.

For example, the set pressure will usually start at the minimumpressure. An initial apnea will lead to new settings for the apnearesponse state and the apnea trigger timer Tc, but not to a change inpressure. The set pressure is the minimum pressure so the comparisonwill not determine “true” because the set pressure has not reduced tothat minimum pressure. Accordingly, the newly set variables Nr and Tcwill not be inadvertently reset by step 496.

If, at step 407 the algorithm determines that the normal breathingcounter has been decremented to 0, this indicates two consecutiveperiods of normal breathing. The algorithm then proceeds to step 408,resets the normal breathing counter to 2 and resets the apnea triggertimer Tc to 0, and most importantly, decrements the apnea response stateNr by 1. The algorithm then proceeds through to step 495.

The normal breathing counter Nd reaching 0 represents two consecutiveperiods of normal breathing. The effect of steps 409 and 410 is to resetthe counter to 2 on any sleep disorder breathing event, meaning anyvalue of the event variable other than normal and none. In particular,at step 409, the algorithm checks whether Event equals “none”. If so, itproceeds directly to step 411. Otherwise, the algorithm proceeds to step410 and resets the normal breathing counter Nd as 2.

The next core branch of the algorithm is to determine which steps toexecute based on the present apnea response state Nr. This isrepresented by steps 411, 414, 423, 431, 441, 447, which determinewhether the algorithm proceeds by associated paths 412 to 413, 415 to421, 424 to 430, 432 to 440, 442 to 446 and 448 to 449 respectively.Each of these paths eventually returns to step 490, but in between mayadjust the apnea response state Nr, the values of timers Tc and Tp andthe value of the event variable.

Step 411 determines whether the apnea response state Nr equals 0 or 5.If so, the algorithm is in a sort of an initial state in which it willwait for a first apnea to occur and proceeds to step 412. If not, thealgorithm proceeds to step 414.

If the algorithm determines at step 412 that Event does not equal“apnea”, then it proceeds directly to step 490 and of course to step495. Otherwise, the algorithm proceeds to step 413. At step 413, thealgorithm increments the apnea response state, sets an apnea triggertimer Tc to a predetermined value, for example 2.5 minutes, and resetsthe event variable to “none”. Resetting Event to “none” means that inthe subsequent pressure adjustment algorithm, there will be noadjustment of the set pressure in response to the apnea that has beendetermined by the event detection algorithm. Resetting event variable to“none” also means that step 490 will determine false and the algorithmwill proceed direct to step 495 without proceeding through steps 491 to493 and looking at the magnitude of any pressure decreases due toarousal.

If the algorithm determined false at step 411, it proceeds instead tostep 414 and determines whether the apnea response state is 1 or 6. Ifthe apnea response state is 1 or 6, the algorithm proceeds to step 415and decrements the apnea trigger timer Tc by an amount equivalent to theloop repeat time for the apnea response algorithm (for example, 20 ms).The algorithm then proceeds to step 416.

At step 416, the algorithm determines whether the apnea trigger time isgreater than 0. The effect of steps 413, 415 and 416 is to only allowincrementing the apnea response state at step 418 if the apnea or nonflow-limited hypopnea (checked at step 417) occurred within 2.5 minutesof the apnea determined at check 412. Otherwise, the algorithm proceedsfrom step 416 to 419 and decrements the apnea response state Nr by 1.This reverts the apnea response state to 0 because no apnea occurredwithin the 2.5 minute trigger window.

Proceeding from step 419 to step 420, the algorithm determines whetherEvent equals “apnea” in the particular execution (with a very lowprobability). If so, the algorithm replaces Event equals “apnea” withEvent equals “none” at step 421.

In the case of a negative determination at step 420, or after theexecuting step 421, the algorithm proceeds to step 490 and therefore tostep 495.

If the timer Tc had not run out at step 416, the algorithm proceedsinstead to step 417 and checks whether the event variable equals “apnea”or “non flow-limited hypopnea”. If not, the algorithm proceeds directlyto step 490 and therefore step 495 without making any furtheradjustments.

If Event does equal “apnea” or “non flow-limiting hypopnea”, thealgorithm proceeds from step 417 to step 418 and increments the apnearesponse state and resets the apnea trigger timer to 2.5 minutes. Theapnea or non flow-limited hypopnea has occurred within 2.5 minutes ofthe apnea found at check 412. Accordingly, the apnea response stateincreases and a new apnea trigger timer is set. Again, the preferredpredetermined value for the apnea trigger timer is 2.5 minutes. Othervalues between, for example, 1 minute or 5 minutes may be appropriate.

The value of the event variable is not reset and remains as “apnea” or“non flow-limiting hypopnea”. Accordingly, the set pressure will beincremented in the pressure adjustment algorithm.

After step 418, the algorithm proceeds to step 490. In this instance,Event may equal “apnea”, so the algorithm may check whether the apneahas occurred during a pressure reduction sequence resulting from patientarousal.

At step 414, if the apnea response state is not 1 or 6, the algorithmproceeds to step 423 and determines whether the apnea response state is2 or 7. If so, the algorithm proceeds to the process of step 424 to 430.These steps are largely similar to steps 415 to 421 for apnea responsestates 1 and 6 except that these steps do not provide for decrementingthe apnea response state Nr by the lapse of time alone (which is theeffect of steps 416 and 419). Instead, the algorithm will remain in thisresponse state (2 or 7) indefinitely unless the response state is eitherincreased (step 427 which will be described shortly) or decreasedelsewhere, such as at step 408 or reset at step 496. As alreadydiscussed, decrementing at step 408 is in response to consecutiveperiods of normal breathing, while eventual resetting at step 496 is inresponse to the set pressure reducing to the minimum pressure.

An increase in the apnea response data at step 427 occurs if an apnea ora non flow-limited hypopnea occurs within the predetermined apneatrigger time of the apnea or non flow-limiting hypopnea determined atstep 417 or the last apnea or last non flow-limiting hypopnea determinedat step 425 while in the present apnea response state. From step 423,the algorithm proceeds to step 424 and decrements apnea trigger timerTc. The algorithm then proceeds to step 425 and checks whether Eventequals “apnea” or Event equals “non flow-limiting hypopnea”. If not, thealgorithm proceeds to step 495. Otherwise, if Event does equal “apnea”or “non flow-limiting hypopnea”, the algorithm proceeds to step 426 andchecks whether the apnea trigger timer is still greater than 0.

If the apnea trigger timer is greater than 0, the algorithm proceeds tostep 427 and increments the apnea response state Nr and then proceeds tostep 428 and resets the apnea trigger timer to the preset apnea triggertime, for example, 2.5 minutes. The algorithm then proceeds from step428 to step 495.

If the algorithm determined at step 426 that the apnea trigger time hadexpired (Tc is equal to or less than 0), the algorithm proceeds to step429 and 430.

If the algorithm determines at step 429 that Event equals “apnea”, thealgorithm resets event to “none” at step 430.

Then, or otherwise, the algorithm proceeds to step 428 and resets thetrigger timer Tc to the predetermined trigger time.

The effect of steps 429 to 430 is to ensure that the pressure adjustingalgorithm does not increment the set pressure in response to the apneathat was found not to have occurred within the apnea trigger time. Theeffect of bypassing step 427 where the apnea trigger timer has expiredat step 426 is that the apnea response state Nr is unchanged. Resettingthe trigger timer at step 428 is either effective when waiting for anapnea or non flow-limiting hypopnea in the next apnea response state, orin the continuing time within the present apnea response state.

If at step 423 the apnea response algorithm determines that the apnearesponse state Nr is not 2 or 7, the algorithm proceeds to step 431 todetermine whether the apnea response state is 3 or 8. If so, thealgorithm proceeds to step 432. Otherwise, it proceeds to step 441. Themethod of steps 432 to 438 is broadly similar to the method of steps 424to 430 except for the inclusion of additional steps 435 and 436 whichprepare an additional pause timer for the next response state.

So proceeding from step 431, the algorithm proceeds to step 432 anddecrements apnea trigger timer Tc. The algorithm then proceeds to step433 and checks whether Event equals “apnea” or Event equals “nonflow-limiting hypopnea”. If not, the algorithm proceeds to step 495.Otherwise, if Event does equal “apnea” or “non flow-limiting hypopnea”,the algorithm proceeds to step 434 and checks whether the apnea triggertimer is still greater than 0.

If the apnea trigger timer is greater than 0, the algorithm proceeds tostep 435 and checks whether the apnea response state Nr equals 3. If Nrequals 3, the algorithm proceeds to set a pause timer Tp. The pausetimer Tp will be active in the next apnea response state. The pausetimer Tp sets the duration of the pause, and in the example Tp is set to5 minutes. the algorithm then proceeds to step 437.

If Nr did not equal 3 at step 435, the algorithm would proceed directlyto step 437.

At step 437, the algorithm increments the apnea response state Nr andthen proceeds to step 438 and resets the apnea trigger timer to thepreset apnea trigger time, for example, 2.5 minutes. The algorithm thenproceeds from step 438 to step 495.

If the algorithm determined at step 434 that the apnea trigger time hadexpired (Tc is equal to or less than 0), the algorithm proceeds to step439 and 440.

If the algorithm determines at step 439 that Event equals “apnea”, thealgorithm resets event to none at step 440.

Then or otherwise, the algorithm proceeds to step 438 and resets thetrigger timer Tc to the predetermined trigger time.

The effect of steps 439 to 440 is to ensure that the pressure adjustingalgorithm does not increment the set pressure in response to the apneathat was found not to have occurred within the apnea trigger time. Theeffect of bypassing steps 435 to 437 where the apnea trigger timer hasexpired at step 434 is that the apnea response state Nr is unchanged.Resetting the trigger timer at step 438 is either effective when waitingfor an apnea or non flow-limiting hypopnea in the next apnea responsestate, or in the continuing time within the present apnea responsestate.

In response states 3 and 8, the algorithm includes an additional stepbetween checking whether the apnea trigger timer has expired andincrementing the response state. This step could be performed afterincrementing the response state with minor adjustment. This step checksthe present response state at step 435 to determine if the next responsestate (the state that will prevail in the next execution of thealgorithm) will be 4.

If the next response state will be 4, for example because the currentresponse state is 3, with the step 435 in the illustrated location, thenat step 436 the algorithm sets a pause time timer Tp with an initialvalue. Preferably the initial value is between 3 minutes and 10 minutesand may, for example, be 5 minutes.

If the next apnea response state will not be 4, then the step of settingthe pause timer is omitted and the algorithm proceeds directly from step435 to 437. If the step of initiating the pause timer is provided afterthe step 437 of increasing the apnea response state, then the equivalentto step 435 would check whether the apnea response state equals 4 ratherthan 3.

Initiating the pause timer from the previous response state could beomitted in favour of a single execution initiation elsewhere in thealgorithm, for example, within the part of the algorithm that isexecuted if the response state is 4. However in that case, correctlysetting and resetting that variable may be more difficult than where itis initiated upon exiting the immediately preceding response state. Aswith equivalent steps 425 and 417, if at step 433 the event is not anapnea or non flow-limited hypopnea, the algorithm proceeds directly tostep 495.

In the preferred embodiment of the invention, two sequences of apnea areallowed for, with a pause state between, and followed by a longer termnon-responsive state. Apnea response state 3 immediately precedes thepause state 4 while apnea response state 8 immediately precedes thenon-responsive apnea response state 9. For the non-responsive apnearesponse state 9, no automatic change of state is provided based on atimer alone. Accordingly, there is no need to set a pause timer.

In iterations where the apnea response state is 4, the algorithm passesthrough steps 411, 414, 423 and 431 and determines at step 441 that theapnea response state equals 4 and proceeds to step 442. The collectionof steps 442 to 446 implements a pause state where the algorithm willnot respond to apneas for a period of time to allow the patient airwayto stabilise. This time is set by the pause timer Tp, which is set atstep 436.

At step 442, the algorithm determines whether the timer has expired bychecking whether Tp is greater than 0. If Tp is greater than 0, then thetimer has not expired and the algorithm proceeds to step 443 anddecrements the timer. The algorithm then proceeds to step 444 anddetermines whether Event equals “apnea”. If Event equals “apnea”, thealgorithm replaces this with Event equals “none” at step 445. If Eventdoes not equal “apnea” at step 444, the algorithm proceeds directly tostep 495. If at step 442, the timer has expired (Tp is less than orequal to 0), then the algorithm proceeds to step 446 and increments theapnea response state so that the next apnea response state will be 5 andin the next iteration the algorithm will look for an apnea to set anapnea trigger timer at step 413.

Where the apnea response state has progressed from state 8 to state 9(at steps 437), in the next iteration the algorithm will proceed throughsteps 411, 414, 423, 431 and 441 and determine at step 447 that theapnea response state is 9. Alternatively step 447 can be omitted,assuming that only apnea response states between 0 and 9 are possible.In that case, the algorithm proceeds to step 448 and checks whetherEvent equals “apnea”. If Event equals “apnea”, the algorithm resetsEvent to “none” at step 449. This ensures that the pressure adjustmentalgorithm does not respond to apneas determined while the apnea responsestate is 9. No other adjustments are made. The apnea response state canonly reduce from 9 by operation of steps 495 and 496 (pressure returningto minimum pressure), steps 402 to 404 (pressure drop due to patientarousal), or steps 405 to 408 (extended periods of normal breathing).

Operating in the manner described, the algorithm can be seen to amendthe Event variable from “apnea” to “none” at steps 413, 421, 430 and 440unless it was preceded by less than 2.5 minutes by another apnea or nonflow-limiting hypopnea. Accordingly, response to a pattern of apneasdoes not commence until an apnea is succeeded by an apnea or nonflow-limiting hypopnea within a period of less than 2.5 minutes. Thisinitial apnea is determined at step 412 and the timer set at step 413.The subsequent apnea, within the timer period, is determined at step417. Otherwise, all other apneas are not responded to due to re-writingEvent to “none” at steps 413 and 421. While the algorithm is in thepause state (Nr equals 4), response to all apneas is suppressed byreplacing Event equals “apnea” with Event equals “none” at step 445.While in a definite non-responsive state (Nr equals 9), response to allapneas is suppressed by replacing Event equals “apnea” with Event equals“none” at step 449.

Accordingly, the algorithm illustrated in detail in FIG. 4 implementsthe principles described earlier, within an overall control where theapnea response algorithm is preceded by an event detection algorithm andsucceeded by a pressure adjusting algorithm. Examples of particularevent detection algorithms and pressure adjusting algorithms are knownin the art.

The event modification algorithm is described here as an example.Modification may be required according to the particular characteristicsof the event detection algorithm and pressure adjusting algorithm. Forexample, if the overall control scheme implements pressure adjustmentsimmediately after determining an event, one appropriate implementationmight involve determining the apnea response by applying the outlinedprinciples against a record of preceding events.

Other overall control architectures for responding to apneasincorporating the present inventions are possible.

The controls according to the present invention may be implemented intypical gases supply systems, in particular in the control programsexecuted in the flow generator. An example system and flow generatorwill be described with reference to FIG. 1 .

FIG. 1 is a block diagram illustrating a preferred embodiment of abreathing gases supply system of a type that may incorporate the presentinvention. The full system includes an apparatus 200 for delivering asupply of breathing gases, a supply conduit 202 and a patient interface204.

The supply conduit 202 extends from an outlet of the gases supplyapparatus to the patient interface.

The patient interface includes a bias flow vent 206 for allowing acontrolled leak from the patient interface 204. The controlled leakallows the inside of the patient interface 204 to be continuouslyflushed by fresh gases supplied by the supply apparatus 200. The patientinterface 204 may comprise any of the many types of typical patientinterface for PAP delivery, for example, nasal mask, full face mask,oral mask, oral interface, nasal pillows, nasal seal or nasal cannula.

The bias flow vent 206 may be located directly on the patient interface,or adjacent the patient interface on a connector between the patientinterface 204 and the supply tube 202 or through the wall of the supplytube 202, close to the patient interface 204. A wide variety of patientinterfaces and conduits are known in the art.

The supply apparatus 200 includes a flow generator. The preferred flowgenerator comprises a fan 210 driven by an electric motor 212. Air isdrawn through an inlet 214 in the housing of the apparatus by the fan210. Pressurised air leaves the fan 210 for supply to the patient.Alternatively, controllable flow generators may draw on a source of highpressure gas, and regulate a flow of gas from the high pressure source.

The apparatus 200 may include a humidifier 216, for example in the formof a pass-over humidifier where air passing through the humidifierchamber picks up a quantity of water vapour from a reservoir of water218. The water reservoir 218 may be heated by a heater 220. Thehumidifier may be integrated with the housing of the flow generator or aseparate, optional, component.

The heater 220 and motor 212 are supplied with power from a power supply222. The amount of power to the motor and the amount of power to theheater are controlled by outputs of controller 224.

The controller 224 is also supplied with power from the power supply222.

The controller 224 receives input from a user interface 226.

The controller 224 may also include an interface 228 for connecting withan external data source. The external data source may, for example, be acommunication interface such as a modem, or may be an interface to anexternal memory such as a smart card, disk drive, flash memory or thelike. For generic use, the interface 228 may be a data communicationport according to any of the many available standards, for example, auniversal serial bus (USB) port. A USB (or similar) interface can beused for connecting a wide range of peripheral devices.

The controller 224 typically includes an embedded microcomputer withstored control programmes.

The controller preferably includes interfaces for receiving input from auser interface 226 and for receiving input from one or more sensorswhich preferably include a flow sensor 230 and may also include apressure sensor 232 downstream of the fan. The flow sensor 230 may beupstream or downstream of the fan.

According to the preferred embodiment of the invention, the apparatus isconfigured to perform control methods in the form of a control programsexecutable by the microcomputer of the controller 224.

Alternatively, the controller 224 may comprise a fixed electroniccircuit implementing the control programs, or a programmed logic circuit(such as an FPGA) implementing the control programme. Electroniccircuits and logic circuits implementing the control programme may bereadily devised by persons skilled in the art.

FIGS. 4 a to 4 c illustrate how the described system responds tohypothetical sequences of events. Each sequence, and the response willbe described briefly. For simplicity, the sequence is limited to threetypes of events, apneas, obstructed breathing and periods of normalbreathing. Apnea events are designated “A”, obstructed breathing events(flow limitations) are designated “O”.

FIG. 4 a illustrates progression from an initial low pressure, through aseries of pressure increases in response to events. The effect of thenon-responsive state is exemplified. In FIG. 4 a , the algorithmresponds as follows:

Event/ Time State/Action 502 No proceeding apnea. Sets trigger time Tcto 2.5 minutes but event resets to None. N_(R) increases to 1. 503 N_(R)increases to 2, Event stays “apnea”, resets trigger timer to 2.5minutes. 504 N_(R) increases to 3, Event stays “apnea”, resets triggertimer to 2.5 minutes. 505 N_(R) stays 3, Event stays “obstructedbreathing”, does not reset trigger. 506 Trigger timer has expired, N_(R)stays 3, Event is overwritten to “None” so pressure does not increase,resets trigger timer. 507 Trigger timer has not expired, N_(R) increasesto 4, Event stays “apnea” so pressure increases, control enterssuppressed state (518). 508 N_(R) stays 4, Event stays “obstruction” sopressure increases. 509 N_(R) stays 4, Event stays “obstruction” sopressure increases. 510 N_(R) = 5, as the suppressed state timer Tp hasexpired. 511 N_(R) = 6, Tc = 2.5 minutes, Event = None, pressure stays.512 N_(R) = 7, Tc = 2.5 minutes, Event stays apnea, pressure increases.513 N_(R) = 7, Tc unchanged, Event stays = Obstructive, pressureincreases. 514 N_(R) = 8, Tc resets to 2.5 minutes, pressure increases,Event stays apnea. 515 N_(R) = 9, Tc = 2.5 minutes, Event stays apnea,pressure increases, indefinite suppression of response to apnea begins.516 Ignored apnea as N_(R) = 9 517 N_(R) = 9, Event stays “obstruction”,pressure increases.

The first non-responsive state is illustrated as period 518 in FIG. 4 a. in this pause state, response to apnea is suppressed, but thealgorithm still responds to obstructed breathing at 508 and 509.

The second non-responsive state is indicated as period 519, whichcommences with the apnea event at 515. In this non-responsive state,response to apneas is suppressed, for example, ignoring the apnea at516, but the algorithm still responds to obstructed breathing at 517.

FIG. 4 b illustrates progression during a sequence of more widely spreadevents. The figure plots set pressure against time. The sequence ofevents and the algorithm response is summarised in the following table:

Event/ Time State/Action 520 Apnea starts timer Tc. Response state goesto N_(R) = 1. 521 Timer Tc expires, response state goes to N_(R) = 0.522 Apnea starts timer Tc. Response state goes to N_(R) = 1. 523 Apneaoccurs before timer Tc expires. Response state goes to N_(R) = 2, Event= apnea is not overwritten, pressure increases. 524 Event = Normal(following 2.5 minutes f normal breathing), N_(d) decrements from 2to 1. 525 Apnea resets N_(d) to 2 and resets timer Tc to 2.5 minutes.There is no increase in response state. Event is overwritten to None, sono pressure increase results. 526 Normal breathing for 2.5 minutes leadsto decrement N_(d) to 1. 527 Normal breathing for 2.5 minutes leads todecrement N_(d) to 0, which leads to N_(R) decrement to 1. The pressurealso decreases (independent of N_(R)) In nearly all cases, the responsestate will immediately change to 0 on next iteration of the algorithm.528 Apnea. N_(R) increases to 1, Tc = 2.5 minutes. Event is overwrittento None, so no pressure increase results. 529 N_(R) stays 1, pressureincreases. Tc unchanged.

The sequence of 4 b shows how the response state can fluctuate up anddown according to frequency of triggering events and can fluctuateindependently of the set pressure.

FIG. 4 c illustrates progression during a period of normal breathing,and during and after two periods of patient arousal. In FIG. 4 c thealgorithm responds as follows:

Event/ Time State/Action 539 The sequence commences with the setpressure at 14 cmH₂O and N_(R) = 9. Accordingly, there is an indefinitesuppression of response to apneas. 540 Responds to obstruction withincrease in pressure to 15 cmH₂O. 541 2.5 minutes after obstruction,normal event is returned, pressure is reduced and Nd reduces to 1. 542N_(R) = 9, Event = Apnea is overwritten to None. 544 Patient arousalresponded to by rapid (0.1 cmH₂O per second) decrease in set pressure.545 Apnea detected. Pressure reduction cycle ends prematurely at 7cmH₂O. Pressure drop P_(D) was 8 cmH₂O. PD >3CMH₂O =>NR resets to 3, andTc set to 2.5 minutes. 546 Another apnea detected. N_(R) increases to 4and apnea is not reset. Pi is set to 4 cmH₂O. Pressure increases by 4cmH₂O. 547 Apnea is ignored as N_(R) = 4 and pause state 556 is ineffect. 548 Obstruction leads to increase in set pressure. 549 Apnea isignored as N_(R) = 4. 550 Apnea is ignored as N_(R) = 4. 557 Pause stateends, N_(R) increases to 5. 551 Apnea is ignored. N_(R) increases to 6.552 Apnea is responded to. Apnea occurred less than 2.5 minutes afterapnea at 551. Response state increases to 7. Pressure is increased. 553Apnea is responded to. Apnea occurred less than 2.5 minutes after apneaat 552. Response state increases to 8. Pressure is increased. 554Patient arousal detected. Leads to a rapid reduction in set pressure.555 Set pressure reaches Pm (3 cmH₂O). NR resets to 0.

What is claimed is:
 1. A PAP apparatus comprising: a gases flow sourceconfigured to supply gases to a patient in use; a sensor configured tosense pressure or flow or both, supplied by the flow source or suppliedto the patient; and a controller configured to receive output from thesensor, determine a plurality of sleep disorder breathing events basedon the output from the sensor, and control an output pressure of theflow source according to a pressure adjusting algorithm based at leastin part on a type of the sleep disorder breathing event detected,wherein the controller is configured to: always respond to flow limitedhypopnea events, respond to non-flow limited hypopnea events up to apressure limit; and only respond to apneas that are non-isolated,wherein only responding to apneas that are non-isolated includesentering a pause state, the pause state being entered based on aprevious number of detected sleep disorder breathing events.
 2. The PAPapparatus of claim 1, wherein the pressure limit is about 10 cmH₂O. 3.The PAP apparatus of claim 1, wherein the pressure limit is less than amaximum pressure limit of the apparatus.
 4. The PAP apparatus of claim1, wherein the apneas are non-isolated if the apneas occur within apredetermined time period of a previous apnea or non-flow limitedhypopnea.
 5. The PAP apparatus of claim 1, wherein the controller isconfigured to only respond to apneas that are non-isolated by increasingthe output pressure or a counter.
 6. The PAP apparatus of claim 5,wherein the controller is configured to enter the pause state inresponse to a total number of non-isolated apneas and hypopneas lessnominal periods of normal breathing exceeding a first threshold.
 7. ThePAP apparatus of claim 1, wherein the controller is configured to exitthe pause state after a predefined duration.
 8. The PAP apparatus ofclaim 1, wherein during the pause state, the controller does notincrease the output pressure in response to apneas.
 9. The PAP apparatusof claim 8, wherein during the pause state, the controller is configuredto increase the output pressure by a predetermined amount in response toflow-limited breaths, flow-limited hypopneas or non-flow limitedhypopneas.
 10. The PAP apparatus of claim 6, wherein the controller isfurther configured to enter a suppressed state in response to a totalnumber of non-flow limited hypopneas and non-isolated apneas lessnominal periods of normal breathing since exiting the pause stateexceeding a second threshold.
 11. The PAP apparatus of claim 10, whereinduring the suppressed state, the controller does not increase the outputpressure or the counter in response to apneas.
 12. The PAP apparatus ofclaim 10, wherein the controller is configured to remain in thesuppressed state until detection of patient arousal or a period ofnormal breathing.
 13. The PAP apparatus of claim 1, wherein thecontroller is configured to always reduce the output pressure inresponse to detection of a period of normal breathing.
 14. The PAPapparatus of claim 1, wherein the gases flow source comprises a blowerand the output of the blower is controlled by the controller.
 15. ThePAP apparatus of claim 1, wherein the gases flow source includes ahumidifier and power input to the humidifier is controlled by thecontroller.